var a = new String('123')
// console.log(a)
a.feng = function () {
    console.log('1232');
    
}
a.feng()
console.log(a);

delete a.feng //删除对象的属性。
console.log(a)
// vue 中添加属性  this.$set(this.form ,'element',123)  this.$delete(this.form, 'element')